The dopamine transporter terminates neurotransmission by reaccumulating dopamine into presynaptic neurons. Cocaine blocks dopamine reuptake by binding to sites on the dopamine transporter and inhibiting its function. Prolonged inhibition of neurotransmitter reuptake potentiates dopaminergic transmission and likely underlies the addictive properties of cocaine. These pharmacological observations and numerous molecular studies have established the clinical importance of the dopamine transporter in psychostimulant abuse. The goal of this work is to identify new chemical entities with specificity for the dopamine transporter. Our primary objective is to develop a functional assay for the dopamine transporter with the capacity to screen combinatorial chemical libraries. Using this assay, we will screen for compounds with cocaine antagonistic properties. We anticipate this small molecule modulators of the dopamine transporter will be candidates for development as therapeutic treatments for drug addiction. To develop a high throughout assay, we will construct yeast strains that express a functional dopamine transporter. These strains, which are stable and amenable to facile manipulations, will serve as screens to identify novel modulators of the dopamine transporter. Lead compounds will be identified by their effects on the growth of strains engineered to require dopamine transporter function. PROPOSED COMMERCIAL APPLICATION: Currently there are no marketed pharmaccuticals that reduce craving and drug-seeking behavior in cocaine addicts. This research has the potential to identify novel chemical entities with selectivity for the dopamine transporter. These compounds will be valuable for developing therapeutic agents for drug abuse and addiction, and possibly for treating Parkinsonian disorders.